JP6480869B2 - Method and apparatus for evaluating bolt tightening force by ultrasonic means - Google Patents

Description

  The present invention relates to a method for performing ultrasonic measurement of a tightening force in a bolt during tightening of a joint including a bolt, and a tightening device for performing the above method.

  When tightening the joint between the bolt and the nut, a tightening force is generated to maintain the joint in a tightened state. This tightening force is produced as a result of the bolt tightening length being deformed or elongated. In general, the tightening operation has two main stages: a first stage in which the bolt is screwed into the nut without deformation, and a joint between the bolt and the nut is established and the bolt is deformed. It can be divided into a second stage. The bolt can be deformed both elastically and plastically. The transition point between the end of the screwing stage and the start of the deformation stage is conventionally shown as a sliding fit.

  In order to optimize the tightening operation, it is desirable to adjust the tightening force generated on the joint. However, it is difficult to directly measure the tightening force. This is because although it is rarely possible, it means that force measuring means must be provided in the joint. Instead, methods have been developed to indirectly measure the clamping force. One such method uses ultrasonic waves to measure bolt elongation. In other methods, the joint is tightened to a certain torque rather than to a certain tightening force.

  In ultrasonic methods, ultrasonic pulsations are transmitted to the bolt and the response time, often taken as flight time, is monitored. The flight time corresponds to the length of the bolt. Thus, a longer measurement of time of flight corresponds to an increase in the length of the bolt and hence the tightening force on the bolt. The time of flight increases linearly with the elongation of the bolt, at least as long as the bolt is simply elastically deformed. However, if the bolt is deformed to such an extent that it begins to deform plastically (which is desirable in certain applications), a new linearity is established. That is, the time of flight increases at a slower rate during plastic deformation than during elastic deformation.

  The problem with the ultrasonic method is the evaluation of the measurement results. First of all, it is difficult to measure the time of flight on a bolt in a cost and time efficient manner before reaching a slip fit in a tightening operation. This is partly because it is difficult to establish a good and sufficient contact between the ultrasonic instrument and the bolt before the port is tightened, ie before the sliding fit. After the sliding fit, the bolt is clamped to the joint and it is very easy to achieve good contact between the ultrasonic instrument and the bolt.

  A conventional way of achieving good contact is to incorporate a contact piece and an ultrasonic pulse generator, for example in the form of a piezoelectric component, in the bolt head. However, this method is a very costly solution and such bolts cost at least 20 times the price of normal bolts.

  It is an object of the present invention to provide a means for evaluating the time of flight at a bolt in a cost and time efficient manner during joint tightening.

  The object of the present invention is achieved by the present invention according to the first and second features.

According to a first aspect of the present invention, the present invention relates to a method for evaluating a tightening force at a screw joint between a bolt and an alignment screw piece during a tightening operation, the method comprising:
A step of tightening the joint with a torque supply device;
Measuring the torque supplied to the joint during tightening;
Simultaneously inducing the ultrasonic pulse in the bolt and measuring the time of flight (TOF) of the ultrasonic pulse in the bolt.
The method further includes
Monitoring torque as a function of rotation angle to determine the rate of torque increase in response to an increase in torque measurement;
Monitoring the time of flight of the ultrasonic pulse as a function of rotation angle to determine the rate of increase of the time of flight of the ultrasonic pulse;
Determining an initial rotation angle of the tightening operation based on the determined rate of increase in torque, where the torque begins to increase as a function of bolt deformation;
Defining the initial rotation angle of the tightening operation as a rotation angle at which the flight time begins to increase;
Determining a total increase in flight time during the tightening operation based on the initial rotation angle of the tightening operation and the rate of increase in the flight time.

According to a second aspect of the invention, the invention relates to a fastening device for fastening a joint comprising at least one bolt and an alignment screw piece,
Such a tightening device is
A shaft for driving the tool device to supply mutual rotation to the bolt and the alignment screw piece; and a torque supply device including a motor for driving the shaft;
The tightening device
A torque measuring device that measures torque as a function of the rotational angle applied to the joint between the bolt and the alignment screw piece during the joint tightening operation;
An ultrasonic transmitter for inducing an ultrasonic pulse on at least one bolt and measuring the time of flight of the pulse on the bolt;
A rotation angle measuring device for measuring a rotation angle (α) between at least one bolt and the alignment screw part during tightening of the joint;
Based on the measured torque, determine the rate of torque increase as a function of rotation angle,
-Based on the measured flight time of the ultrasonic pulse, determine the rate of increase in flight time as a function of the rotation angle,
・ Based on the increase rate determined by the torque, determine the initial rotation angle at which the torque starts to increase due to the deformation of the bolt,
Defining the initial rotation angle as a rotation angle at which the flight time begins to increase;
And a control unit configured to determine a total increase in flight time during the tightening operation based on the initial rotation angle and the rate of increase in flight time.

  In a special embodiment of the invention, the step of determining the rate of increase in torque comprises a first instantaneous torque at the first special rotation angle of the tightening operation and a subsequent first step at the second special rotation angle of the tightening operation. Monitoring the second instantaneous torque and performing a linear approximation, the initial rotation angle is estimated from the linear approximation, and corresponds to an angle where the torque is equal to zero.

  In another embodiment of the invention, the step of determining the rate of increase of the time of flight of the ultrasonic pulse comprises the first instantaneous flight time at the first relevant rotation angle of the tightening operation and the second related rotation angle of the tightening operation. Monitoring the subsequent second instantaneous flight time at and performing a linear approximation.

In yet another embodiment of the present invention, the established clamping force at the joint is evaluated based on the total increase in time of flight, and the clamping force is expressed by the formula F = k ₁ · ΔTOF (k ₁ is the bolt geometry It is considered proportional to the total increase in flight time according to the bolt's constant constant depending on the shape and material.

  In one embodiment of the invention, following the calculation of the tightening force, the tightening operation is controlled to end at the scheduled target tightening force, the total increase in flight time is continuously monitored, and the tightening force is Calculated continuously from the monitored increase in flight time.

  In another embodiment of the invention, the tightening operation is controlled to end at the scheduled target torque, the total increase in flight time is monitored, and when the tightening operation is completed while meeting the planned target torque, The tightening force can be calculated from the monitored total increase in flight time.

  In yet another embodiment of the present invention, the tightening operation is paused at the first associated rotation angle of the tightening operation, and a first instantaneous value of the time of flight of the ultrasonic pulse is measured at this rotation angle.

  All special embodiments of the invention can be implemented as special steps that can be made to be performed by the control unit in the method of the invention or in the clamping device of the invention.

  Other features and advantages of the present invention will be apparent from the drawings and detailed description of the illustrated embodiments.

  In the following detailed description, reference is made to the accompanying drawings.

Diagram showing the torque T as a function of the mutual rotation angle α of the bolt and the alignment screw piece during a tightening operation. Diagram showing the clamping force F as a function of the mutual rotation angle α of the bolt and the alignment screw piece during a tightening operation. The figure which shows the volt | bolt and nut in the initial stage of a screwing operation | work. The figure which shows the volt | bolt and nut of FIG. 3 when a nut is fastened firmly to a volt | bolt. 1 is a block diagram illustrating an embodiment of a method according to the present invention.

  The diagram of FIG. 1 shows the tightening operation according to the invention. This diagram shows the torque T as a function of the angle of rotation α between the first and second thread pieces during the tightening operation of the joint comprising the first and second thread pieces.

The joint is illustrated by a bolt 10 and a nut 11 in FIGS. In this example, the nut 11 is screwed into the bolt 10 and the sponge piece 12 is fastened between them. In this example, the actual tightening operation is shown in a simplified manner in order to show variations in the torque T and the tightening force F as a function of the rotation angle α. In FIG. 3, the nut 11 is located at the loose end of the bolt 10, and in FIG. 4, the nut 11 is gradually screwed to the target rotation angle α _target corresponding to the desired target tightening force F _target .

As can be seen in the diagram of FIG. 1, when the nut 11 is screwed into the bolt 10, the torque T is close to zero during the initial stage A of the tightening operation. During this initial phase A, the torque T simply depends on the friction between the bolt 10 and the nut 11. When the nut 11 is screwed at the rotation angle α ₀ so as to come into contact with the sponge piece 12, the sponge piece 12 is squeezed by further movement of the nut 11 and the torque T starts to increase. In the second stage B after tightening, the sponge piece 12 functions as a complete spring and its passive “spring force” increases linearly in proportion to the squeezing. Accordingly, the tightening force F at the joint increases linearly as a function of the rotation angle α during the second stage B of the tightening operation. In the illustrated embodiment, the clamping force F is elastic as a result of increased pressure from the sponge piece 12 acting on the head 13 of the bolt 10 with a barrel (not shown) between the head 10 of the bolt 10. To be stretched. The clamping force F is opposed to the spring force of the sponge piece 12 but is equally large.

  Now, referring to FIG. 1, the torque T required to turn the nut 11 relative to the bolt 10 is proportional to the axial force of the bolt 10 and the screw pitch, so that it is linear during the second stage B of the tightening operation. To increase. In the illustrated example, the screw pitch of the bolt 10 is the same along the entire length of the bolt 10, so that the torque T is linearly proportional to the axial force due to the spring force of the sponge 12 along the entire length of the bolt 10.

The torque T can be continuously monitored by a torque meter included in the torque supply device. The torque supply device may be a torque wrench such as a nut runner or a power tool. It is possible to control the tightening towards a special target torque T _target , which is common in the art. Usually, it is desirable to achieve a certain target tightening force F _target at the joint instead of the special target torque T _target . However, the problem is that the clamping force F cannot be measured directly by the torque supply device. Instead, the clamping force F is estimated from the measured torque T or indirectly measured, for example by ultrasonic pulses.

  In the present invention, the clamping force F is measured indirectly by measuring the time-of-flight TOF of the ultrasonic pulse in the bolt 10. The time of flight TOF of the ultrasonic pulse corresponds to the time required for the ultrasonic pulse to travel through the bolt 10 and return. Therefore, the time of flight TOF represents the length of the bolt. Thus, the total increase in flight time ΔTOF corresponds to the elongation of the elastic part of the bolt according to a known relationship that depends on the geometry and composition of the bolt. In practice, the total increase in flight time ΔTOF is not only dependent on the elongation of the bolt, but also on the tension induced in the bolt 10, so that the increased tension in the material is the time of flight TOF of the ultrasonic pulse. Cause an increase. The relationship of what is the increased time of flight ΔTOF corresponding to increased tension or bolt elongation in each material is bolt specific and must be empirically tested for each particular bolt type, There is no need to test for each special type of bolt. Typically, one-third of the total increase in flight time ΔTOF corresponds to the actual elongation of the bolt and the remaining two-thirds corresponds to increased tension in the material.

  In FIG. 2, the tightening force F at the joint is shown as a function of the mutual rotation angle between the first screw piece and the second screw piece during the tightening operation. The tightening force F is directly proportional to the total increase in flight time ΔTOF. The problem with measuring the time of flight TOF is that it is not clear to know the total increase in flight time ΔTOF because it is difficult to determine the rotation angle at which the time of flight ΔTOF begins to increase. This is because it is difficult to establish the necessary solid connection between the bolt head and the ultrasonic transmitter when screwing the bolt at low torque.

As a result, the first measurement TOF1 time of flight is measured by the rotation angle corresponding to the rotation angle alpha _'1 in which the first associated that is positioned in the second stage in the B tightening work beyond the snug fit . That is, at this rotational angle, a connection is established between the ultrasonic transmitter and the bolt head. In a special embodiment of the invention, the tightening operation can be interrupted until it guarantees that the first measurement TOF ₁ of the time of flight is correctly measured. The first measurement TOF ₁ of the time of flight corresponds to the clamping force F ₁ at the first associated rotation angle α ′ ₁ . At this point, it is possible to evaluate the actual clamping force F ₁ correctly impossible. This is because, as described above, the initial flight time TOF ₀ corresponding to the length of the bolt 10 before the bolt 10 is extended and deformed is not known. On the other hand, once the connection is established, it is possible to continuously monitor the increase in the time-of-flight TOF and thus the clamping force F. In other words, it is possible to estimate the increase rate dTOF / dα of the flight time TOF as a function of the rotation angle α.

The present invention, without the need to measure the initial flight time TOF _0, provides a way to find the initial flight time TOF _0. That is, by using the measured value of the torque T, the initial rotation angle α ₀ of the elastic deformation of the bolt corresponds to the rotation angle at which both the torque T and the tightening force F start to increase linearly. It is possible to estimate the initial rotation angle α ₀ of the elastic deformation. The initial rotation angle α ₀ can be found by estimating the torque T curve as a function of the rotation angle α. The initial rotation angle α ₀ of the elastic deformation of the bolt is the rotation angle at which the elastic deformation of the bolt is started and thus the torque T is equal to zero.

In a special embodiment of the invention, the method comprises the following steps:
(1) In order to determine the increase rate dT / dα of the torque T according to the increase of the measured torque T, the first instantaneous torque T ₁ is monitored at the first special rotation angle α ₁ and the second special torque a second step of monitoring the instantaneous torque T ₂ at Do rotation angle [alpha] 2.
(2) To determine the rate of increase in flight time dTOF / dα, the first instantaneous value TOF ₁ of the time of flight of the ultrasonic pulse is monitored at the first relevant rotation angle α ′ ₁ and the second relevant Monitoring the second instantaneous value TOF ₂ followed by the time of flight of the ultrasonic pulse at the rotation angle α ′ ₂ . The associated rotation angles α ′ ₁ , α ′ ₂ that monitor the time-of-flight TOF may or may not be the same as the special rotation angles α ₁ , α ₂ that measure the torque T. In FIG. 2, not the time of flight TOF but the clamping force F is shown as a function of the rotation angle α. This is possible because the clamping force F is directly proportional to the total increase in flight time ΔTOF. Thus, the curve showing the time of flight TOF as a function of the rotation angle α is the same except for the slope of the curve and the position along the Y axis. However, in the curves shown in FIG. 2, these differences are not apparent because the axes are shown without size, so neither the physical slope of the curves nor the position of the curves along the Y axis is shown.
(3) initial rotation angle alpha ₀ of tightening operations decided, the step of torque in the initial rotation angle alpha ₀ starts to increase as a function of the deformation of the bolt. In the illustrated example, this is done assuming that the curve is linear, so the initial rotation angle α0 is to estimate the curve backward from the two rotation angles [α ₂ , T ₂ ] and [α ₁ , T ₁ ]. Can be found in In other forms of the invention, the torque T may have another dependence on the rotational angle α. However, in most cases, the torque T increases linearly with respect to the rotation angle α, so that the increasing rate dT / dα of the torque T is constant.
(4) The initial rotation angle α ₀ of the tightening operation is defined as a rotation angle at which the flight time TOF starts to increase in order to determine the total increase ΔTOF of the flight time during the tightening operation. The clamping force F at the joint can be directly induced from the bolt ratio factor and the total increase in time of flight ΔTOF.

With the inventive method described above, the tightening operation can be controlled towards a special target tightening force F _target . As shown in FIGS. 1 and 2, it is also possible to estimate a target rotation angle α _target that should end the tightening operation. The target rotation angle α _target can be determined without defining the initial rotation angle α ₀ as the rotation angle at which the time of flight TOF begins to increase. Instead, the clamping force F can be calculated based on the difference in the rate at which the torque T and the clamping force F increase as a function of the rotation angle α, respectively, and on the instantaneous value of the torque T.

In a special embodiment of the invention, it is sufficient to monitor the time-of-flight TOF or the rate of increase of the torque T as a function of the rotation angle α. That is, when both the increase rate dTOF / dα of the flight time TOF and the increase rate dT / dα of the torque T are known as a function of the rotation angle α, in order to estimate the tightening force F from the instantaneous value of the flight time TOF, It is sufficient to know the torque T at one special rotation angle α ′. This means that the clamping force F is directly proportional to the time-of-flight TOF according to the equation (1) F = k ₁ · TOF, where k ₁ is the bolt ratio constant depending on the bolt geometry and composition. It is possible because it is known. Further, the clamping force F is proportional to the torque T according to the equation (2) F = k ₂ · T (where k2 is equal to the ratio of dF / dα divided by dT / dα).

  From the above equation, it is possible to estimate the tightening force Fα at the angle α from the monitored torque value Tα or the monitored value of the time of flight TOFα at a specific rotation angle α. Therefore, in principle, it is possible to infer tightening by monitoring the time-of-flight TOF or the torque value T and evaluating the tightening force F by either equation (1) or equation (2).

Regardless of which special method is used, the target clamping force F _target can be reevaluated throughout the entire clamping operation. For example, more than two special rotation angles required to determine the slope of each curve can be included to determine both the instantaneous clamping force F and the target clamping force F _target as accurately as possible during the clamping operation. .

  The present invention has been described with respect to one specific embodiment. However, the present invention is not limited to this embodiment. It will be apparent to those skilled in the art that other embodiments can be practiced within the scope of the invention as defined by the claims.

10 bolt 11 nut 12 sponge part 13 head of bolt 10 A initial stage B second stage T torque α rotation angle α ₀ rotation angle α1
α ′ ₁ first related rotation angle α ₂ second special rotation angle α ′ ₂ second related rotation angle α _target target torque F tightening force F _target
Rate of increase in TOF flight time TOF ₀ percentage increase of the initial flight time ΔTOF first measurement value of the total increase in TOF ₁ flight time of flight time dTOF / dα flight TOF dT / d [alpha] torque T

Claims (7)

A method for evaluating a tightening force (F) at a screw joint between a bolt and an alignment screw part during a tightening operation,
A step of tightening the joint with a torque supply device;
Measuring the rotation angle (α) between the bolt and the alignment screw piece during tightening of the joint;
Measuring the torque (T) supplied to the joint during tightening;
Simultaneously inducing an ultrasonic pulse in the bolt and measuring the time of flight (TOF) of the ultrasonic pulse in the bolt;
Monitoring the torque (T) as a function of the rotation angle (α) to determine the rate of increase (dT / dα) of the torque (T) in response to an increase in the measured value of the torque (T);
Determining the initial rotation angle (α ₀ ) of the tightening operation where the torque (T) starts to increase as a function of the deformation of the bolt based on the determined rate of increase (dT / dα) of the torque (T) , An initial rotation angle (α ₀ ) is estimated from the rate of increase (dT / dα) of the torque (T), and the torque (T) corresponds to an angle equal to zero ;
In a method comprising:
Monitoring the time of flight (TOF1) of the ultrasonic pulse as a function of the rotation angle (α) to determine the rate of increase (dTOF / dα) of the time of flight (TOF) of the ultrasonic pulse;
Defining the initial rotation angle (α ₀ ) of the tightening operation as the rotation angle at which the time of flight (TOF) begins to increase;
Determining a total increase in flight time (ΔTOF) during the tightening operation based on the initial rotation angle (α ₀ ) of the tightening operation and the rate of increase (dTOF / dα) of the flight time (TOF);
・ Evaluate the established tightening force (F) at the joint based on the total increase in flight time (ΔTOF), and the tightening force (F) is expressed by the formula F = k1 ・ ΔTOF (k1 is the bolt geometry and material) A step that is considered proportional to the total increase in time of flight (ΔTOF) according to
A method comprising the steps of: The step of determining the increase rate (dT / dα) of the torque (T) includes the first instantaneous torque (T ₁ ) at the first special rotation angle (α ₁ ) of the tightening operation and the second special of the tightening operation. Monitoring the subsequent second instantaneous torque (T ₂ ) at the correct rotation angle (α ₂ ) and performing a linear approximation, the initial rotation angle (α ₀ ) is estimated from the linear approximation and the torque (T 2. The method according to claim 1, characterized in that) corresponds to an angle equal to zero. The step of determining the rate of increase (dTOF / dα) of the time of flight (TOF) of the ultrasonic pulse consists of the first instantaneous flight time (TOF ₁ ) and the tightening at the first relevant rotation angle (α ′ ₁ ) of the tightening operation. _3. Monitoring the subsequent second instantaneous time of flight (TOF ₂ ) at a second relevant rotation angle (α ′ ₂ ) of work and performing a linear approximation. The method described. Following the calculation of the clamping force (F), the clamping operation is controlled to end at the scheduled target clamping force (F _target ), the total increase in flight time (ΔTOF) is continuously monitored, and the clamping force 2. The method of claim 1, wherein (F) is calculated continuously from a monitored increase in flight time ([Delta] TOF). The tightening operation is controlled to end at the scheduled target torque (T _target ), the total increase in flight time (ΔTOF) is monitored, and the tightening operation is completed while meeting the planned target torque (T _target ). 2. Method according to claim 1, characterized in that the clamping force (F) is sometimes calculated from the monitored total increase in flight time ([Delta] TOF). The tightening operation is paused at the first associated rotation angle (α ′ ₁ ) of the tightening operation, and the first instantaneous value (TOF ₁ ) of the time of flight of the ultrasonic pulse is measured at this rotation angle. The method according to any one of claims 1 to 5. A tightening device for tightening a joint including at least one bolt and an alignment screw piece,
A shaft for driving the tool device to supply mutual rotation to the bolt and the alignment screw piece; and a torque supply device including a motor for driving the shaft;
The tightening device
A torque measuring device that measures torque as a function of the rotational angle applied to the joint between the bolt and the alignment screw piece during the joint tightening operation;
An ultrasonic transmitter for inducing an ultrasonic pulse on at least one bolt and measuring a time of flight (TOF) of the pulse on the bolt;
A rotation angle measuring device for measuring a rotation angle (α) between at least one bolt and the alignment screw part during tightening of the joint;
In a tightening device having
-Based on the measured torque (T), the rate of increase in torque (T) (dT / dα) is determined as a function of the rotation angle (α),
-Based on the measured time of flight (TOF), the rate of increase in time of flight (TOF) (dTOF / dα) is determined as a function of the rotation angle (α),
The initial rotation angle (α ₀ ) at which the torque (T) starts to increase due to the deformation of the bolt is determined based on the determined increase rate (dT / dα) of the torque (T), and the initial rotation angle (α ₀ ) Estimated from the rate of increase of torque (T) (dT / dα), corresponding to an angle where torque (T) equals zero;
Defining the initial rotation angle (α ₀ ) as the rotation angle at which the time of flight (TOF) begins to increase;
-Based on the initial rotation angle (α ₀ ) and the increase rate (dTOF / dα) of the flight time (TOF), the total increase (ΔTOF) of the flight time (TOF) during the tightening operation is determined,
・ Evaluate the established tightening force (F) at the joint based on the total increase in flight time (ΔTOF), and the tightening force (F) is expressed by the formula F = k1 ・ ΔTOF (k1 is the bolt geometry and material) Having a control unit adapted to be considered proportional to the total increase in time of flight (ΔTOF) according to the ratio constant of bolts depending on
Tightening device characterized by.

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